Brain waves are active when dying, and the brain may be reminiscing about life

　　Some people have been on the brink of death, and when they recall their near-death experiences in the future, they will say that many things they have experienced in their lives flashed through their minds, like a "marquee".

　　What kind of brain activity does a person experience before dying?

This has been a mystery for centuries.

Until recently, a research team finally obtained a continuous EEG of a dying human and observed a strange sight.

　　Scientists even speculate that when a person is about to leave, his brain is really looking back on life.

　The highest frequency brain waves

　　Obtaining data on the brain activity of dying people is not in the researchers' plan.

　　An 87-year-old man in Canada was admitted to the emergency room after a fall.

Doctors discovered he had an intracranial hematoma and performed a craniotomy to remove the hematoma.

After surgery, the patient was stable for two days, but then developed a series of symptoms that could be seen as worsening neurological function.

　　So doctors decided to continuously monitor his condition with an EEG, from which 12 seizures were confirmed.

But in the process of monitoring, the patient suddenly died of a heart attack.

The old man had signed a waiver of first aid, so his brain activity was more purely recorded during the journey to death.

　　With the permission of the patient's family, the scientists obtained a total of 900 consecutive seconds of brain wave data.

The data included a seizure that occurred around the 200th second.

At the 470th second, the neural activity of the left hemisphere was suppressed; at the 694th second, the neural activity of the left and right hemispheres was suppressed; at the 720th second, the patient suffered cardiac arrest.

　　Usually, when a patient's heart stops beating for more than 30 seconds, he can be pronounced dead.

Therefore, the 30 seconds before and after the cardiac arrest (the 720th second) has become the time period that researchers are most concerned about.

　　Scientists analyzed the brain waves of the old man and were surprised to find that when the neural activity of the left and right brains was suppressed (the 694th second), the gamma waves did not weaken immediately, but instead increased, and did not fall back until after cardiac arrest.

What does this phenomenon represent?

　　Neurons in our brains rely on electrical signals to transmit information to each other, and the waveforms generated by these signals are brain waves.

Human brain waves can be divided into five categories according to the level of frequency, named after the five Greek letters of delta, theta, alpha, beta and gamma.

　　Among them, the slowest is delta wave, the frequency is below 4 Hz, and adults only have this type of brain wave during sleep; the fastest is gamma wave, with a frequency of 30-150 Hz, which is similar to some advanced brain waves. Functions such as cognition and memory are closely related.

　　Usually, when people are highly focused and busy processing information, the brain produces more gamma waves.

The strength of gamma waves means that the brain is working hard.

If the level of gamma waves in the human brain is low for a long time, there may be problems with attention, memory and learning ability.

　　But why are these gamma waves, which are used to perform advanced tasks, summoned at the end of life?

　　May be recalling life

　　Brain waves of different frequencies sometimes interact with each other.

When a high-frequency brain wave (small period) encounters another low-frequency brain wave (large period), the amplitude of its vibration may be affected by the latter.

　　The phenomenon of brain waves of different frequencies interacting is called cross-frequency coupling.

In reality, many different ways of coupling across frequencies can occur, some in frequency modulation (FM) and some in amplitude modulation (AM), like a radio.

　　From the 87-year-old's EEG, scientists also observed the interaction of other brain waves with gamma waves: both the cross-frequency coupling of alpha and gamma waves, and the cross-frequency coupling of theta and gamma waves coupling.

Among them, the coupling of alpha waves and gamma waves is very prominent.

　　The coupling of alpha waves and narrow-band gamma waves (30-60 Hz) was strongest during the period of suppressed left brain activity (starting at 470 seconds); and after cardiac arrest (starting at 720 seconds), The coupling of alpha waves and broadband gamma waves (80-150 Hz) is strongest.

　　The team says the interaction of alpha and gamma waves is known to be involved in cognitive processes and recall in healthy humans.

The study's corresponding author, Ajmal Zimmer of the University of Louisiana speculates: "The brain at the time of death may be relying on those brain waves to retrieve memories, and in just a few seconds, the last time to review the important things in life. fragment."

　　When a patient goes into cardiac arrest, the power of each type of brainwave begins to drop.

But when scientists made a horizontal comparison among the five types of brain waves, they found that the power of gamma waves, which are most relevant to advanced brain functions, still increased after the heart stopped.

　　In 2013, scientists observed the brain activity of dying rats under controlled conditions in the laboratory and found a similar phenomenon: within 30 seconds after cardiac arrest, gamma waves appeared for a short time , and there is a tight coupling with both alpha waves and theta waves.

　　As for why the gamma waves increase, the researchers believe that it is caused by hypercapnia before cardiac arrest and cerebral blood flow cessation after cardiac arrest.

　　Combined with the new findings, scientists suggest that dying brains may execute a biological process that may have been preserved across species over the course of biological evolution.

　　Of course, the new study has some flaws. For example, it used only one human EEG sample, and it was from a human with severely damaged nervous systems.

A person's dying brain waves may not be typical, and may not necessarily be generalized to more humans.

　　In addition, Professor Anil Seth, a neuroscientist at the University of Sussex in the United Kingdom, believes that only by the enhancement of gamma waves and the interaction of gamma waves with other brain waves, it is impossible to determine that the brain is flashing back to life. various pasts.

That's just a possibility.

　　But at the same time, he admits, the findings are "both moving and fascinating."

After all, it would be difficult for scientists to obtain that precious EEG data if the patient's condition had not developed unexpectedly.

It is ethically impossible to systematically collect the brain activity of dying humans.

　　(According to "Global Science") (author chestnut)